Ratio meters usually also include a fixed vessel containing a damping liquid with the magnet being immersed therein.
Each of the coils generates a magnetic field proportional to the current passing therethrough. The magnet takes up a position along the resultant of the fields. For a two-coil ratio meter, the angle defined by the indicator needle relative to an origin position is thus determined by the relationship tan.sup.-1 (I.sub.1 /I.sub.2) in which I.sub.1 and I.sub.2 represent values proportional to the ampere-turns carried by each of the coils.
In the car industry, large-deflection ratio meters are generally used for displaying a speed or a number of engine revolutions per minute. Large-deflection ratio meters generally include a return coil spring fixed to the shaft.
The structure and operation of ratio meters are well known to the person skilled in the art and are therefore not described in greater detail below.
The present invention relates more particularly to the control means designed for applying appropriate electrical signals to the coils of a ratio meter.
Numerous control means have already been proposed for this purpose, for example in the following patent documents: U.S. Pat. No. 2,057,845, DE-A-853 181, U.S. Pat. No. 2,500,628, U.S. Pat. No. 3,168,689, U.S. Pat. No. 3,327,208, U.S. Pat. No. 3,329,893, U.S. Pat. No. 3,624,625, U.S. Pat. No. 3,636,447, U.S. Pat. No. 3,732,436, U.S. Pat. No. 3,946,311, U.S. Pat. No. 4,051,434, U.S. Pat. No. 4,070,665, DE-A-2 924 617, U.S. Pat. No. 4,230,984, and EP-A-0 218 737.
The object of the present invention is to provide novel control means enabling ratio meter accuracy to be improved while remaining simple in structure and reasonable in price.
Another object of the present invention is to provide control means making it possible to operate with a display over 360.degree..